Nest-site fidelity, body weight and population size of the red mason bee, Osmia rufa (Hymenoptera : Megachilidae), evaluated by Mark-Recapture experiments

Mark-recapture experiments were used to examine nest-site fidelity, natural local population size and effects of body weight on dispersal strategies in the solitary bee Osmia rufa Linnaeus 1758. A total of 974 hibernated females was individually marked and weighed inside their cocoons and then released in five orchard meadows for emergence. In May 2002. colonisation of three spatially separated trap nest locations on each study site (mean distance 52 m) by marked and unmarked females of O. rufa was monitored. Only 222 (22.8 %) of all marked females (3-108 per site) were re-observed. Mortality rates varied between 2.2 and 26.4 % between study sites. Thus estimated 74 %, of emerged females leaved the parental nest-site. The number of observed unmarked females varied between 9 and 16 per-site resulting in an estimated natural Population size between 48 and 258 individuals or 15 females per 1000 m(2) on average. The mean body weight of marked recaptured females (113.0 +/- 14.9 mg) was significantly higher than the body weight of marked but not recaptured females(107.3 +/- 19.0 mg). The results give new insights into the possible densities of natural populations of a solitary bee species, its nest-site fidelity and the potential role of body weight for dispersal strategies.